This invention relates to sheet containing polyvinyl butyral (PVB) and more particularly to the roughened surface of such sheet and to a process for producing it.
Plasticized sheet containing PVB is known as an impact-dissipating layer for use with glass or rigid plastic panels (hereinafter "laminating panel(s)") in laminated safety glazings.
It is likewise known to roughen the major planar surface(s) of such sheet to facilitate deairing during preparation of such laminated glazings. More particularly, minute channels between the smooth surface of the laminating panel and the extremities of minute valleys in the face of a rough surface of the contiguous PVB sheet permit air between the two members to escape when pressure or vacuum is applied to the interface.
U.S. Pat. No. 4,654,179 discloses crosslinked PVB for generating surface roughness during extrusion. A single PVB phase is used with roughness described therein as a function of PVB molecular weight distribution, the broader the distribution obtained by increasing the crosslink level, the lower the magnitude of surface roughness. In such '179 patent, crosslinked and uncrosslinked PVB are chemically, molecularly integral in a homogenous mass. According to this patent, roughness is adjusted by changing crosslinking agent concentration used during synthesis of the PVB, the greater such concentration the lower the sheet roughness.
While this technique has been successful, it would be desirable to provide a more versatile way to regulate PVB sheet roughness using crosslinked PVB which does not solely rely on changing the chemistry of the resin during its synthesis.